Safety pilot detector



June 11, 1957 RAVNSBECK '2,795,270

SAFETY PILOT DETECTOR 2 Sheets-Sheet 1 Filed June 23, 1954 Inventor FRED RAVNSBECK June 1957 F. RAVNSBECK SAFETY PILOT DETECTOR 2 Sheets-Sheet 2 Filed June 25, 1954 lfzvenior; FRED RAVN BECK Unimd States o 7 2,795,270 SAFETY PILOT DETECTOR Fred Ravnsbeck, Oaklawu, Ill. Application June 23, 1954, Serial No. 438,678

' 2 Claims. or. 158-423) This invention relates to burner safety systems for fuel burners. V In fuel burners such as boilers, heaters and the like, utilizing either liquid orgaseous fuel, it is customary to aflord a safety control system that includes a gas pilot burner, and means for sensing such pilot burner and controlling the main fuel supply means such as the main fuel supply valve so that the main fuel supply is discontinued when the absence of an effective pilotflame is sensed. Such pilot flames may be of the continuously operating type, or may be intermittent, in which case igniting means are afforded in accordance with usual practice. a Moreover, many different forms of flame sensing means may be utilized, such for example as a flame sensing rod which is associated with an electronic control system responsive to the sensed presence or absence of a flame of a predetermined size, or such sensingmeans maybe of the temperature sensitive, light sensitive or vibration sensitive type. V p 7 p While safety control systems that have heretofore been used have been satisfactory under most operating conditions, it has been determined in practice that the flame sensing means utilized are in many instances unable to determine accurately when a pilot flame has become too small to properly ignite the main burner of thesystem. Such a condition may arise where the gas pressure that is supplied to the pilot burner is unduly reduced, and when this happens, it has been foundthat the pilot'flame'may in many instances become too small to ignite the main burner, and yet will be of a sufficient size or intensity to cause the flame sensing means to indicate the presence of a satisfactory pilot flame. Such a conditionisobviously unsafe, and it has resulted in the application of a safety test that is known as the turn-down test, in which the gas pressure is progressively reduced to a value that is considerably below the normal gaspressure that is available. Burner safety systems asheretofore used have been unable to meet such tum-down tests in a satisfactory manner, and in view of this, it is the primary object of the present invention to enable burner safety systems to meet the turn-down test, and to enable this to be accomplished in a simple and economical manner. More specifically, it is an object of the present invention to enable conventional flame sensing equipment to be utilized in substantially the same way as heretofore used, but toenable such conventional flame sensing equipment to afford a more accurately defined degree of safety control. Other and related objects of the present invention are to aiford an improved burner safety system,,to provide a pilot burner unit that may be utilized in standard installations that have heretofore been made, and to afford such a unit which will enable these prior installations to attain satisfactory compliance with the turn-down test as hereinabove described. a

Other and further objects of the present invention will be apparent from the following descriptionand claims and are illustrated in the accompanying drawings which,

Patented June 11, 1957 by way of illustration, show a preferred embodiment of the presentinvention and the principle thereof and what I now consider to be the best mode in which I have contemplated applying that principle. Other embodiments of the invention embodying the same or equivalent prin- 'ciple may be used and structural changes may be made as desired by those skilled in the art without departing from the present invention and the purview of the appended claims. I

In the drawings; I a H V a Fig. 1 is a schematic plan sectional view showing 'the burner safety control embodying the present invention in association with afuel burner; I v

Fig. 2 is a view similar to Fig. 1 illustrating the relationship of the two pilot flames when a reduced gas pressure is encountered; I I a I p a Fig. 3 is a longitudinal sectional view of the safety p qt v Fig. 4 is a longitudinal sectional view taken substantially along the line 44 of Fig.3;

Fig. 5 is a front end view of the unit;

Fig. 6 is aperspective view showing another installation wherein a different type of flame sensing means is employed; 7 a I Fig. 7 is a view of the safety pilot unit of Fig. 6, the view being partiallyin longitudinal section; and

Fig. 8 is a sectional view taken longitudinally on Fig. 7 along the line 8'-8.

For purposes of disclosure, the invention is herein illustrated in Figs. 1 to 5 as embodied in a safety pilot unit 10 that is diagrammatically shown as being mounted in operative position in the wall of a combustion chamber 11 in which a main fuel burner 12 is located. This safety pilot unit 10 is shown in detail in Figs. 3 to 5 of the drawings, and comprises a base 15 that may be formed as by casting from a metal such as aluminum, and the base 15 h'as'an enlarged head 15H and a reduced longitudinally projecting portion 15R. The reduced portion 15K is adapted to be fitted into and secured in place in a conventional mounting sleeve 16 that may form a part of the burner installation, and which is ordinarily mounted in a fixed position in a wall of the combustion chamber 11. The base 15 has a longitudinal fuel mixing chamber 17 formed therein as by means of a bore extended longitudinally into the inner end surface 15E of the base, and a pilot fuel inlet is afforded by an inlet sleeve 18 that extends through the head 15H and longitudinally into the chamber 17. The pilot fuel such as gas is discharged from the discharge end 18E of the sleeve 18 longitudinally into the chamber 17 and is mixed with air that enters through an air inlet passage 19, thereby to form a relatively lean fuel mixture within the chamber 17. Such air may be drawn into the passage 19 by aspiration, or maybe forced into the passages from a suitable source. This fuel mixture isutilized under the present invention to afford a common fuel source for a pair of related but dilferently sized burners ports 20S and 20L, and these two burner ports are provided on and as a part of a common burner sleeve 21 that is formed from a metal such steel and isthreaded as at 21T into the inner end of the fuel chamber 17.

a The fuel mixture in the chamber 17 is thus supplied at the same pressure and the same richness to both of the burner ports 20S and EL, and as will be evident in Figs. 3 andS, these two burner ports are afforded by a relatively heavy plug 22 in the end of the burner sleeve 21, the burner port 20L being afforded by a relatii/ely large diameter opening 22L in the plug 22, while the ports will aflford a relatively large main pilot flame 120L from the burner port 20L and a relatively small or secondary flame 1208 from the pilot burner port 208. These two flames 1208 and 120L are related .in size, and this general relationship is maintained throughout any variations thatmay take place in the fuel pressure supplied to the mixing chamber 17. Thus the flames may bear the relationship shown in Fig. 1 during the normal operation of the system, while upon substantial reduction of the gas pressure, these flames may bear the relationship shown in Fig. 2 of the drawings. Under the present invention, the safety control of the main burner is attained by sensing the small or secondary flames 1208 and accomplishing this sensing operation in such a way that the main pilot flame 120L will have no controlling effectiveness on and with respect to the flame sensing means.

Thus, in the form of the invention illustrated herein,

the sensing means is shown as being one of the wide variety of flame sensing devicesin common commercial use, such sensing means being shown as constituting a flame sensing rod 25 mounted ina suitable insulator 126 that is, in turn, mounted by means including a brass sleeve 127 in a longitudinal bore 128 formed in the base member 15. This flame sensing rod 25 has the inner end 125 thereof bent laterally so as to be disposed within the path of the secondary flame 1208, as will be evident in Figs. 1 and 3, and the relationship of this sensing means to the burner port 208 is such that when the secondary flame 1208 is reduced to a relatively small size as shown, for example, in Fig. 2 of the drawings, such secondary flame 1208 will no longer be effective upon the flame sensing rod 25. Even when the secondary flame 1208 is reduced to such a small size, the main pilot flame 120L will be relatively large, but the comparative sizes of the two flames are so related that the sensing operation will render the fuel burner system inoperative as soon .as the size of the main pilot flame 120L has reached a size that is so small as to be dangerous.

In the present embodiment of the invention, an igniter in the form of a spark plug 30 is illustrated, but it will be recognized that such an igniter is an optional characteristic and is not essential to the present invention.

As pointed out hereinabove, the sensing means that sense the secondary flame 1208 are etfectually isolated from the main pilot flame 120L, and in the present instance this is accomplished through the provision of a separator plate 35 that is mounted on the inner end of the burner sleeve 21 so as to be disposed between the two flames. The divider plate 35 is of a suflicient width to prevent the main pilot flame from lapping about the edges thereof and into the sensing zone 225 that is afforded adjacent the sensing means 25, and hence the sensing means 25 are responsive only to the size or intensity of the secondary flame 1205.

For purposes of disclosure, the invention is herein illustrated in Figs. 6 to 8 as embodied in a safety pilot unit 310 that is diagrammatically shown as being mounted in operative position in the wall of a combustion chamber 311 in an operative relation to a main fuel burner such as an oil burner 312. This safety pilot unit 310is in most respects like the unit 10, and where the elements are identical, the same reference characters are employed. Thus the unit 310 is shown in detail in Figs. 7 and 8 of the drawings, and comprises a base 15 formed as previously described with an enlarged head 15H and a reduced longitudinally projecting portion 15R. The reduced portion 15R is mounted as described in a conventional mounting sleeve 16 that may form a part of the burner installation, and which is ordinarily mounted in a fixed position in a wall of the combustion chamber 11 at one side of the main burner 312.

The base, 15 has the same longitudinal fuel mixing chamber 17 and pilot fuel inlet sleeve 18 that extends through the head 15H and into the chamber 17. The

pilot fuel such as gas is discharged from the discharge end 18E of the sleeve 18 longitudinally into the chamber 17 and is mixed with air that enters through an air inlet passage 19, as hereinbefore described. The air may be drawn into the passage 19 by induction, or may be forced into the opening 19 by a suitable connection with a blower or the like, and this fuel mixture is fed to the burner ports 20S and 20L that are afforded by a common burner sleeve 21 that is of the kind described hereinbefore.

The two burners will afford a relatively large main pilot flame L from the pilot burner 20L, as described hereinbefore, and in the form of the invention shown in Figs. 6, 7 and 8, the safety control of the main burner is attained through the use of another form of sensing unit 325 that senses the small or secondary flame 1205 in such a way that the main flame 120L will have no controlling effectiveness on and with respect to the flame sensing means. The sensing means 325 may be any one of the wide variety of flame photo-electric sensing devices in common commercial .use where the photo-sensitive element is focused on the flame area that is to be sensed. One such sensing unit may be identified as the Firetron photoconductive cell manufactured and sold by Combustion Controls Corp., 720 Beacon Street, Boston 15, Mass. Thus the sensing unit 325 has its mounting body disposed in the longitudinal bore 128 formed in the base member 15 and is held in place by set screw 326. The sensing unit 325 has its forward end 325E disposed adjacent to the location of the pilot flame 1208, and in this relation the sensing unit 325 will sense the presence of the flame 1208 so long as such flame 1208 is of its normal size. However, when the secondary flame 120$ goes out, or is reduced to a relatively small size, such secondary flame 1208 will no longer be effective upon the flame sensing unit 325.

It is important to note that the sensing unit 325 that senses the secondary flame 1208 are effectually isolated from the main pilot flame 120L, and as shown in Figs. 7 and 8, this is accomplished through the provision of a separator plate 335 that is mounted .on the inner end of the burner sleeve 21 so as to be disposed between the two flames as in the previously described embodiment, but n Figs. 7 and 8, the plate 335 is made of substantially greater width and length so as to effectually shield the sensing unit 325 from the large pilot flame.

Since the secondary flame 1208 under the present invention is not required to function as an igniting means and functions solely as an indicator or measure of the size of the main pilot flame 120L, such secondary flame 1208 may be arranged to be extremely responsive to gas pressure variations so that the secondary flame will be reduced to a small size, or even extinguished in a much more responsive manner than the ordinary main pilot such as those heretofore used. Thus it will be evident that the conventional sensing means and control means may be rendered more effective when used in accordance with the present invention.

It has been found in practice that the burner safety control that is thus afforded under the present invention meets the turn-down test in a practical and effective manner, and accomplishes this in such a way that the pilot burner unit of the present invention may be utilized in the same way but with more satisfactory results than the pilot burner installations heretofore employed.

Thus, while I have illustrated and described the preferred embodiment of my invention, it is to be understood that this is capable of variation and modification, and I therefore do not wish to be limited to the precise details set forth, but desire to avail myself of .such changes and alterations as fall within the purview of the following claims.

I claim:

1. In a burner safety system, a gaseous fuel source,

.aburner sleeve having at one end portion thereof an air inlet passage and a connection to said fuel source and having a pair of substantially parallel closely adjacent outlet passages formed in the other end portion thereof for discharging combustible mixture outwardly from said sleeve in substantially parallel paths, one of said passages being relatively large in cross section and being adapted to afford a main pilot burner for producing a main pilot flame, and the other of said passages being relatively small in cross section and being adapted to afford a secondary burner for producing a secondary flame substantially smaller than the main pilot flame, an elongated shield including a plate mounted on said sleeve and extending from a position between the outlets of the passages and substantially parallel to said passages whereby to separate the main and secondary flames discharging from said passages, and flame sensing means adapted to be normally impinged by the tip of said secondary flame and disposed solely on the same side of the shield as the relatively smaller passage and positioned inwardly from the free end of said shield whereby said flame sensing means is isolated from the main pilot flame by said shield.

2. In a burner safety system, a mounting sleeve, a base mounted at one end of said sleeve and having a mixing chamber therein opening into said mounting sleeve, a gaseous fuel inlet sleeve secured to said base and projecting into said mixing chamber and said body having an air inlet opening therein communicating with the mixing chamber, :a burner sleeve fixed to said base within said mounting sleeve and projecting from the opening of said mixing chamber longitudinally within the mounting sleeve, said burner sleeve having a pair of substantially parallel closely spaced outlet passages formed in the free end thereof for discharging combustible mixture outwardly from said sleeve in substantially parallel paths extending longitudinally outwardly of the mounting sleeve, one of said passages being relatively large in cross section and being adapted to afford a main pilot burner for producing a main pilot flame, and the other of said passages being relatively small in cross section and being adapted to afford a secondary burner for producing a secondary flame substantially smaller than the main pilot flame, an elongated shield including a plate mounted on said burner sleeve between said passages and extending from a position between the outlets of the two passages and substantially parallel to the passages longitudinally within the mounting sleeve whereby to separate the main and secondary flames discharging from said passages, and flame sensing means adapted to be impinged by said secondary flame mounted on said base and disposed solely on the same side of said shield as the relatively smaller passage and terminating inwardly from the free end of said shield whereby said flame sensing means is isolated from the main pilot flame by said shield.

References Cited in the file of this patent UNITED STATES PATENTS 2,032,045 Branch et al Feb. 25, 1936 2,236,609 Ray Apr. 1, 1941 2,319,351 Shipley et a1. May 18, 1943 2,544,930 Malek Mar. 13, 1951 2,667,920 Smith Feb. 2, 1954 2,688,363 Tarrico Sept. 7, 1954 FOREIGN PATENTS 68,234 Denmark Dec. 27, 1948 

